Control device for activating a switch

ABSTRACT

A control device for activating a switch is disclosed. This device comprises a contractile sensing element sensitive to the concentration of ions in a body of water. The switch is activated in response to a predetermined change in the length of the contractile sensing element. The device is especially useful in initiating regeneration of water-softener devices.

United States Patent [72] inventors William Hodes Rahway; EdwardStudley, North Plainfield, both of NJ. Appl. No. 505,921 Filed Nov. 1,1965 Patented Nov. 23, 1971 Assignee American Standard Inc.

New York, N.Y.

CONTROL DEVICE FOR ACTIVATING A SWITCH 5 Claims, 6 Drawing Figs.

U.S. Cl ZOO/61.04, 210/96, 210/500 Int. Cl H01h 36/00, Bold 15/04 Fieldof Search 210/96,

[56] References Cited UNITED STATES PATENTS 3,172,037 3/1965 Pfeifier210/96 X 3,250,392 5/1966 Luck 210/96 3,305,805 2/1967 Tann 335/2052,748,687 6/1956 Ballard ZOO/61.04 X 3,163,729 12/1964 Flagg ZOO/61.04

Primary Examiner-Samih N Zaharna Assistan! Examiner-Thomas G. WyseAttorneys-Sheldon H. Parker, Tennes 1, Erstad and Eyre,

Mann & Lucas ABSTRACT: A control device for activating a switch isdisclosed. This device comprises a contractile sensing element sensitiveto the concentration of ions in a body of water, The switch is activatedin response to a predetermined change in the length of the contractilesensing element. The device is especially useful in initiatingregeneration of water-softener devices.

PATENTEnunv 23 um SHEET 2 0F 4 VALVE VALVE 24 VALVE CONTROL DEVICE FORACTIVATING A SWITCH This invention relates to water treatment. Inparticular, this invention relates to water softening or deionization bythe use of beds of ion-exchange resins, natural or synthetic zeolites,or the like.

It is common practice in the water treatment art to purify water bypassing it through beds or columns filled with ionexchangematerialsfTypically, in industrial practice, at least two columns areused, or two sections of a single column, to provide at least twotreatment sections. In one of these sections, a cation-exchange materialis used as the column packing. Such a cation-exchange material may be,for example, a resinous composition having fixed anions in combinationwith exchangeable'cations, which may be, for example, hydrogen or sodiumions. As the water percolates through the bed of cation-exchange resin,those cations in the water that are responsible for making it hard areexchanged for the exchangeable ions of the resin, so that the treatedwater emerging from the cation-exchange column contains acids or sodiumsalts in place of the calcium, magnesium and other salts originallypresent in the water.

Following treatment by the cation-exchange resin, the water is usuallypassed through a second column or zone in which it is subjected to theaction of an anion-exchange resin. The anion-exchange resin may be, forexample, a resinous composition having fixed cations in combination withan exchangeable anion, usually chloride or hydroxyl ion. As the waterdischarged from the cation-exchange column is percolated through theanion-exchange column, the anions corresponding to the acids or sodiumsalts therein are exchanged for the exchangeable anion in theanion-exchange resin.

Normally, when the exchangeable ion in the cationexchange resin used ishydrogen ion, the anion-exchange resin used is one in which theexchangeable ion is the hydroxyl ion. In this case, the metal salts areconverted in the cationexchange column to the corresponding acids, andthe acids are converted in the anion-exchange column to water. Theproduct of such a purification system is known as deionized ordeminerialized water.

Whenthe exchangeable ion in the cation-exchange column is sodium, it isusual to use an anion-exchange column packed with a resin in which theexchangeable ion is chloride. In such a system, the cation-exchangecolumn converts salts of other cations calcium, magnesium, etc.) to thecorresponding sodium salts, and the anion-exchange column converts thesodium salts (sodium carbonate, sulfate, etc), to sodium chloride. Theproduct of such a system is known as softened water. Softened water,unlike deionized water, has a mineral content in the form of sodiumchloride. Water-softening systems, as opposed to deionization systemshave the advantage, however, that both the cation and the anion-exchangeresins can be regenerated with brine solution, whereas deionizationsystems require the use of two different solutions, both of which aremore expensive than brine -for example a solution of strong acid, suchas H,SO, or HCl, to regenerate the ion-exchange resin, and a solution ofa strong base such as NaOH to regenerate the anionexchange resin.

The present invention is equally applicable to deionization systems andto softening systems. It is herein described, as a matter ofconvenience, primarily with respect to water-softening systems.

In either deionization systems or in water-softening systems as abovedescribed, it is in the nature of the process that the cation and anionexchange resins eventually lose their effective exchange capacity byvirtue of the fact that all or a substantial part of the exchangeableions have been replaced by ions removed from the water being treated.Thus, the available sodium ions in the cation-exchange resin of awater-softening system are eventually replaced to a large extent bycalcium, magnesium andother ions extracted from the water, and theavailable chloride ions have been largely replaced by carbonate,sulfate, and other anions from the water. When this condition isreached, the exchange resins are no longer effective to remove theundesired ions from the water, and the resins must be regenerated. Inthe case of water-softening systems as above described, this is done byflooding the resins in the columns with brine solution. The exchangereactions involved are reversible, and flooding the resins with brineresults in a reverse exchange, whereby the calcium, magnesium, etc. inthe cation-exchange column are replaced by fresh sodium ions, and thecarbonate, sulfate, etc. in the anion-exchange column are replaced bynew chloride ions. The used brine solution containing the impurity ionsoriginally extracted from the water treated, may then be exhausted towaste.

Although the above description has referred to systems in which thecation-exchange resin and the anion-exchange resin are contained inseparate columns, it is also common practice to pack both resins into asingle column, either in separate zones or as a uniform mixture ofresins, and the invention is equally applicable to systems of thesingle-column type.

It is necessary to control, in some fashion, the point at which theregeneration cycle is activated. The simplest way is to sample thesoftened water periodically, analyze it for a measurable characteristicrelated to the effectiveness of the softening action (such as pl-l,conductivity, or calcium concentration, for example) and initiate theregeneration cycle when the measured characteristic indicates that theion-exchange capacity of the beds is exhausted, or approachingexhaustion. This method is unsatisfactory. in practice for mostapplications, because it requires regular attention on the part of theoperator and consumes time in the making of the necessary measurements.Except for special applications where water is used in small volume oronly intermittently, this method is therefore prohibitively expensive.

Other water-softening systems have been so designed that theregeneration cycle is initiated automatically after a specified timeperiod, or after the treatment of a predetermined volume of water.These, too, have proven less than satisfactory in practice. The systemswhich initiate the regeneration after a predetermined time fail tocompensate for fluctuations in water demand which mayplace a larger orsmaller load on the ion-exchange capacity of the resins in a given timeperiod. Those which initiate the regeneration after a predeterminedvolume of water has been treated fail to compensate for fluctuations inthe salt content of the input water. In either case there is a danger onthe one hand of regenerating the resins before it is needed, which iswasteful of time, power and regenerant solution, or on the other hand ofpassing water through resins that are overdue for regeneration,resulting in incomplete softening of the water and contamination of theinternal water system, e.g., boilers, heaters, by water scale formingelements.

Another and more recent approach to the problem of automaticallyinitiating the regeneration at an appropriate time has been to embedelectrodes constituting a conductivity cell, pH meter, or the like inone of the ion-exchange columns or to place them in the softened watereffluent line so that they measure the characteristics of the watercontinuously, or on an automatically controlled periodic schedule, andto associate them with appropriate circuitry such as to be automaticallyinitiate the regenerating cycle when the measured characteristic of theeffluent water passes a predetennined control value. Such systems haverepresented a very successful partial solution to the problem. However,they are in generaldependent on the electrical measurement of very smallchanges in conductivity or other measurable characteristics of theion-exchange material or of the effluent purified water. The equipmentfor making measurements of such small changes in characteristics isexpensive in its simplest form and, unless made in more sophisticatedforms that are even more costly and delicate, is subject to error causedby gradual changes in the characteristics of the electrodes, minoralterations of the electrolyte, fluctuations in line voltage, and thelike.

An object of this invention, therefore, is to provide an improvedcontrol device for a water-softening apparatus.

Another object is to provide an improved apparatus for the softening ofwater. 1

Still another object is to provide an improved sensing element useful ina control device for water-softening apparatus.

Another object is to provide an improved method of operating awater-softening system.

A more particular object is to provide water-softening apparatus andcontrol apparatus therefor, that operate automatically, withoutrequiring attention from an operator.

Another object is to provide apparatus for the control of awater-softening system that compensates for fluctuations in waterdemand.

Yet another object is to provide apparatus of the type described, whichcompensates for fluctuations in the impurity content of the input water.

A further object is to provide apparatus for the control of awater-softening system, which does not depend on sensitive electricalmeasurements or costly and delicate electrical apparatus for the sensingof characteristics of the ion-exchange resins or the effluent softenedwater.

A feature of the invention is the use of a sensing element comprisingcontractile fibers sensitive to calcium ion concentration.

Another feature is the use of an electromechanical assembly foractivating an electrical circuit in response to a change in the lengthof a fibrous sensing element.

A further feature resides in the use of particular contractile fiberscomposed of copolymers or mixtures of polymers of polycarboxylic acidsand polyhydroxy macromolecules, as more fully described hereinafter, andin methods for preparing such fibers.

Yet another feature resides in the employment of a novel method for thecontrol of initiation of a water-softener regeneration cycle, the methodbeing more fully described hereinafter.

Other objects. features and advantages of the invention will becomeapparent from the following more complete description and claims, andfrom the accompanying drawings.

In one particularly desirable embodiment, this invention contemplates awater-softening apparatus comprising in combination cationexchange meansfor removing divalent cations from water to be treated and substitutingfor said divalent cations, cations selected from the group consisting ofhydrogen ions and sodium ions, anion-exchange means for removingdivalent anions from said water and substituting for said anions, anionsselected from the group consisting of hydroxyl ions and chloride ions,sensing means located in said apparatus in the flow stream of said waterat a point downstream of at least a portion of said cation-exchangemeans, said sensing means being sensitive to the concentration ofcalcium ions in said water, means for regenerating said cationexchangemeans and said anion-exchange means, means for regenerating said sensingelements, and means responsive to said sensing means for activating saidregenerating means in response to a predetermined level of calcium ionconcentration in said water.

In another particularly desirable embodiment, this inventioncontemplates a control device for a water-softening apparatus,comprising in combination sensing means comprising a contractile sensingelement sensitive to the concentration of calcium ions in a body ofwater surrounding said sensing element, and control means responsive tosaid contractile sensing element for controlling the operation of saidwater-sofiening apparatus in response to a predetermined change in thelength of said contractile sensing element.

In another aspect, this invention contemplates a sensing element usefulin control apparatus for water-softening and water-deionizing apparatus,comprising in combination at least one contractile fiber having avariable length responsive to the concentration of calcium ions in abody of water surrounding said fiber, and a pair of end fittings on saidfiber adapted to immobilize one end of said fiber and to transmit toassociated control apparatus changes in the position of the other end ofsaid fiber, and the means of resetting said fibers to their originallength and ionic state by regenerative ionic solutions.

In still another particularly desirable embodiment, this inventioncontemplates a contractile fiber comprising an interpolymer ofpolyacrylic acid with polyvinyl alcohol in approximately equalproportions by the weight.

Another especially desirable aspect of this invention contemplates amethod of operating a water-softening system, comprising in combinationthe steps of passing water to be softened through a mass ofcation-exchange resin and a mass of anion-exchange resin, at theappropriate point subsequent to at least part of said passage throughsaid cation-exchange resin immersing in said water a sensing elementcomprising a contractile fiber having a variable length responsive tothe concentration of calcium ions in said water, and regenerating saidcation-exchange resin whenever the length of said fiber signals acalcium ion concentration in excess of a predetermined value. The meansof regenerating the cation-exchange will also serve to regenerate thesensing element fibers to the original set size and ionic environment.

Referring now to the figures:

FIG. 1 is a diagrammatic representation of a water-softening systemaccording to the invention.

FIG. 2 is a somewhat diagrammatic representation of a control assemblyaccording to the invention, including the novel sensing element of theinvention.

FIG. 3 is a schematic diagram of one form of electrical circuitry thatmay be used in conjunction with the apparatus of FIGS. 1 and 2 to carryout an automatically controlled regeneration cycle.

FIG. 4 is a diagrammatic representation of another form ofwater-softening system according to the invention, having a sensingdevice embedded in the ion-exchange material.

FIG. 5 is a somewhat diagrammatic perspective view, with certain partscut away, of another form of control assembly according to theinvention.

FIG. 6 is a graphical illustration of the manner in which thecontractile fiber of the invention changes in length in response tochanges in calcium ion concentration in the surrounding water.

As illustrated in FIG. 1, the water-softening system according to thisinvention comprises an input water line 10; preferably provided with apressure gauge 12 and one or more filters for removing solid matter,such as stone filter 14 and Pall filter 16. In the normal operation ofthe system for the softening of water, the water to be treated entersthe system through water line 10, through pressure gauge 12 and filtersl4 and 16, and passes through normally open, solenoid-controlled valve18, into ion-exchanger column 20. Solenoid-controlled valves 22 and 24are closed during the water-softening operation. On emerging from theion-exchanger column 20, the softened water passes through line 26 tocontrol chamber 28. In chamber 28, the treated water surrounds a sensingelement comprising contractile fibers 30. A magnet 32 is suspended fromcontractile fibers 30, in such a way that the magnet is raised as thefibers contract. A reed or switch or the like, contained in housing 34is responsive to the position of magnet 32. Emerging from the top ofcontrol chamber 28, the treated water passes through line 36, normallyopen solenoidcontrolled valve 38 and manual valve 40 to the point ofuse. A storage tank (not shown) may be interposed betweensolenoid-controlled valve 38 and manual valve 40 if desired, as will beobvious to those skilled in the art.

The water softening operation continues in the manner just describeduntil the calcium ion concentration of the treated water reaches apredetermined value, which may be selected at will and adjusted by therelative positions of the contractile fibers and the magnet 32 attachedthereto, and the elements in housing 34 which are responsive to theposition of magnet 32.

When the calcium ion concentration reaches the predetermined value, thefibers 30 contract to an extent sufficient so that magnet 32 closesswitch 42 (FIG. 2), contained in housing 34, which, through suitableelectrical connections (not shown in FIGS. 1 and 2) initiates theregeneration cycle.

FIG. 2 illustrates in greater detail the sensing element and the switchmeans contained in housing 34. As shown in FIG. 2,

housing 34 contains a reed switch having a leaf 42 made of 5 magneticmaterial, or carrying a separate piece of soft iron or the like (notshown), which is mounted in position such that when the fibers 30 are intheir extended condition, the magnet 32 is in a position indicated bydotted lines where it is incapable of affecting leaf 42, so that switchleaf 42 remains open, as indicated in dotted lines. When fibers 30contract in response to an increase in the calcium ion concentration ofthe surrounding water in chamber 28, the magnet 32 moves upwardly to theposition shown in solid outline, in which it draws switch leaf 42 to theclosed position indicated by solid lines in FIG. 2. The closing of theswitch indicates the regeneration cycle, as more fully explained belowwith reference to FIG. 3. In order to enable the contraction of fibers30 to bring about the required change in the position of magnet 32, thefibers are provided with appropriate end fittings 44 which are suitablyconnected to a suspension linkage 46 to a fixed member such as rod 48 atthe upper end of the fibers, and a connecting link 50 at the lower endof the fibers, whereby magnet 32 is suspended.

As will be evident to those skilled in the art, many other arrangementsmay be used for the purpose of causing the switch or its equivalent torespond to a contraction of contractile fibers 30. To mention a fewvariations, the magnet may be mounted on switch leaf 42, a piece of softiron or the like being suspended from the fibers in place of magnet 32.In place of a magnetically operated switch, a mechanically operatedmicroswitch may be used, or a capacitance-sensitive device responsive tothe position of a piece of iron or the like suspended from the fibers,or a linear transducer responsive to a contractile force exerted by thefibers, etc.

The regeneration cycle may be carried out in various ways, andcontrolled by various circuit arrangements, as will be obvious to thoseskilled in the art. One such circuit arrangement is illustrated in FIG.3. In the operation of the regeneration cycle by the control apparatusas illustrated in FIG. 3, the regeneration cycle is initiated by thecontraction of fibers 30 closing switch 42. Switch 42 energizes timermotor 45. Timer motor 45, preferably a synchronous motor or the like, isconstructed either directly or through suitable reduction gearing, torotate at a suitable speed (for example I revolution in 30 minutes), ashaft (not shown) bearing five cams (also not shown), shaped andpositioned to open and close cam-follower switches 47, 49, 50, 52 and54, in appropriately timed sequence to carry out the regeneration cycleabout to be described.

The closing of switch 42 also energizes pilot light 56. Immediately onthe energization of timer motor 42 a first cam closes switch 47 andholds it in closed position until the completion of the remainder of theregeneration cycle, so that pilot light 56 indicates that theregeneration cycle is in progress.

After a small time interval, for example l minute, a second cam closesswitch 49 which in turn activates the solenoids (not shown) ofsolenoid-controlled, normally open valves 18 and 38, although This cutsoff all flow of water through the apparatus, as will be obvious oninspection of FIG. 1, as valves 18 and 24 are both closed. Switch 49also energizes pilot light 58.

After a further short interval (e.g. 2 minutes) a third cam closesswitch 50. The closing of switch 50 energizes relay 60 which, in turn,energizes pilot light 62, and the solenoids (not shown) associated withnormally closed, solenoid-controlled valves 22 and 24. Raw water nowflows (see FIG. 1) from the feed line through filters l4 and 16 and line64, thence through valve 24 and upwardly (in opposition to the normalflow direction) through'ion-exchange column 20, washing out soliddeposits, and finally through valve 22 to waste. This backwash iscontinued for an appropriate period of time, for example about 5-l0minutes.

At the end of the backwash period, the third cam opens switch 50, thusdeenergizing relay 60, which deenergizes pilot light 62, and allowsnonnally closed valves 22 and 24 to close.

Next, a fourth cam closes switch 62, which energizes relay 66. Relay 66,in turn, activates brine-regeneration step is in progress, and alsoactivates salt pump 70 and pilot light 72, which indicates that the saltpump is in operation, and reopens valve 22. During this phase of theoperation, the salt pump circulates brine from brine tank 74 throughcheck valve 76, downwardly through control chamber 28, through line 26,upwardly through ion-exchange column 20 and through valve 22 to waste.Brine is pumped through in this fashion for a suitable period, forexample 5 minutes, and then the fourth cam opens switch 52, closingvalve 6 and deactivating salt pump 70. The brine solution inion-exchange column 20 and control chamber 28 is allowed to stand understatic conditions for a suitable time period, say 4 minutes. Then thethird cam, operating through switch S0 and relay 60, reopens valves 22and 24 allowing raw water to flow through line 64, valve 24, column 20and valve 22 to the drain, thus flushing the ion-exchange column 20 freeof brine. The flushing operation continues for a suitable time, say 4minutes, after which the third cam recloses switch 50, deenergizingrelay 60 and allowing valves 22 and 24 to close.

Finally, the second cam reopens switch 48, allowing normally open valves18 and 38 to reopen, restoring normal operation. At the same time, thefirst cam reopens switch 46, thereby deenergizing timer motor 44 andpilot light 56 and thus indicating the end of the regeneration cycle.

FIG. 4 illustrates a modified form of water-softening apparatusaccording to the invention, using a sensing element which is embedded inthe ion-exchange resin. Using this form of the invention, theregeneration cycle can be automatically initiated when the bed isapproaching exhaustion, before there is any appreciable change in thecharacteristics of the treated water.

In the operation of the apparatus as illustrated in FIG. 4, hard waterto be treated enters through line 10 which is preferably provided withpressure gauge 12, and passes through filters l4 and 16. In normaloperation, solenoid valves 18 and 78 are open, and the water flowsdownwardly through ionexchange column 20, passing the control elementindicated generally at 80, through normally open valve 78, upwardlythrough flow meter 82 (optional), and through flowcontrol valve 40 tostorage or use.

As the softening action continues, the exchange capacity of the resin incolumn 20 is gradually depleted, first at the top of the bed and thenprogressively downward. The control element is located preferably in thelower portion of the column. As the moving front of depleted resincapacity reaches the point at which the sensing element of the controlis located, the calcium ion concentration of the water in this portionof the bed increases signaling that the bed is approaching exhaustion,and initiating the regeneration cycle.

For the regeneration cycle, valves 22 and 24 are first opened and valve18 and 78 closed, backwashing the ion bed with raw water to remove soliddeposits. Then valve 24 is closed and brine is pumped from brine tank 74by brine pump 70 through check valve 76, upwardly through ion-exchangecolumn 20 through valve 22 to waste. Finally, the residual brine isflushed out of the column by backwashing with raw water, using the samevalve settings as for the initial backwash. If desired, the initialbackwash may be omitted, as the circulation of brine and the subsequentbackwash will adequately remove any foreign solid materials that mayhave been deposited in the bed. Valve 84 is not essential to theoperation of the apparatus, but may be provided for sampling purposes.

Obviously, the regeneration cycle of the apparatus of FIG. 4 may becontrolled by an automatic control arrangement similar to that of FIG.3.

FIG. 5 illustrates, somewhat diagrammatically, a suitable type ofcontrol assembly for use with the apparatus as shown in FIG. 4. As shownin FIG. 5, the control assembly comprises an array of contractile fibers30 mounted in a tubular housing pilot light 68, signaling that the 86,shown in phantom, adapted to be inserted through a suitable aperture inthe side of an ion-exchange column (not shown in this view). Housing 86is not watertight, but is perforated in the vicinity of fibers 30 toallow the water in the column to flow around the fibers. One end of thebundle of contractile fibers 30 is connected to the inside end ofhousing 86. The other end of the fiber bundle is connected to a cord orwire 88 which extends to the interior of housing 90, which is locatedoutside the wall of the column.

Within housing 90, the wire or cord 88 is connected to one end of a barmagnet 92, which is mounted for limited rotation about a pivotal axis94. Suitable means (not shown), are provided for biasing magnet 92 toresist rotation in the direction produced by tension on cord or wire 88.Such means may be, for example, a coil spring, a weight attached to themagnet, or simply the gravitational bias which may be generated bylocating the pivot at a point other than the center of gravity of themagnet.

Outside the housing is a second bar magnet 96, which is pivotallymounted in a suitable fixed member 98, in such a position that it tendsto rotate in response to rotational movements of magnet 92, keepingitself in alignment therewith. Magnet 96 may be, for example, mounted ona shaft (not visible) joumaled in fixed member 98.

On the other end of such a shaft, or otherwise fixed to magnet 96, is amercury tilt-switch 100, connected by suitable electrical leads 102 tothe regeneration cycling circuit (not shown in this view).

In operation of the control assembly as shown in FIG. 5, the mercuryswitch is normally open. When the calcium ion concentration of the watersurrounding contractile fibers 30 increases above a predetermined value,fibers 30 contract, exerting a tension on cord or wire 88 which, inturn, causes a partial rotation of magnet 92 about axis 94. Magnet 96follows the rotation of magnet 92, causing, in turn, a partial rotationof tilt switch 100, closing it and energizing the regeneration circuit.By the time the regeneration is complete, the contractile fibers 30 haverelaxed sufiiciently to return magnet 90, magnet 96, and tilt-switch 100to their nonnal positions, thus resetting the control for the next cycleof operation.

From the foregoing description, it will be apparent that thewater-softening system and the control assembly of this invention may beused with any sensing element embodying a contractile fiber whichcontracts appreciably in the presence of calcium ions. Calcium is notthe only water-hardening ion that must be removed by the water-softeningsystem. Other cations, such as magnesium, strontium, aluminum and thelike, and anions such as carbonate and sulfate ions must also beremoved, and it is theoretically possible to have a water effluent whichis undesirably hard, without containing an excess of calcium ions. Invirtually all practical applications, however, calcium is the mostabundant and troublesome of the hardening ions present, and can safelybe used as an index of the total hardness of the water.

A particularly desirable and effective fiber for use in the sensingelement according to the invention is an interpolymer or a mixed polymerof polyacrylic acid and polyvinyl alcohol. Such a fiber may be producedfor example, by spinning or extruding into a coagulating bath a mixtureof polyvinyl alcohol and polyacrylic acid solutions.

Many other polyelectrolytes which contain carboxy and hydroxy radicalssensitively react to the presence of alkaline earth ions, such ascalcium and magnesium. Often water soluble polyelectrolytes formexceedingly weak or brittle structures when coagulated from solution andsubsequently dried. In order to translate changes in polymerconfiguration into macroscopic dimensional changes polyelectrolytes arereinforced by the coagulation together with other polymers andstrengthened by intermolecular cross-lining.

Products with increased tensile and rupture strengths are obtained bycodissolving polyelectrolytes such as polyacrylic acid, polymaleic acidwith hydroxyl bearing polymers such as polyvinyl alcohol, hydroxyethylcellulose, carboxymethyl cellulose, polypropylene oxide, hydroxylatedrubbers, partially esterified cellulose acetate. The polymer mix iscoagulated in suitable nonsolvents and the precipitates are cast as filmor spun as fibers. Heating at l20 C. for l0 minutes to 3 hours serves tostabilize the interpolymer structure by crosslinking. The extent ofcross-linking and thus the extent of subsequent dimensional changes inwater media can be controlled by the length of time the polymers areexposed to temperatures in this range.

Copolymerization of the electrolytes containing monomers, viz, maleicanhydride, acrylic acid, or methacrylic acid, etc. with vinyl acetate,styrene, vinyl methyl ether, acrylamide, acrylonitrile, vinyl chloride,ethyl acrylate, etc., can provide hardness sensitive materials.Coprecipitation with hydroxy polymers, such as polyvinyl alcohol,provides the necessary strength characteristics. The incorporation of0.2 percent to 5 percent polyfunctional cross-linking agents, such asdivinyl benzene, ethylene glycol dimethacrylate, hexamethylol melamine,etc. serve to stabilize the copolymer product fibers.

The coagulating bath may be, for example, a mixture of sodium sulfateand zinc sulfate in aqueous solution.

The process conditions for making such fibers may vary widely, as willbe readily apparent to those skilled in the art of spinning syntheticfibers. The following example, therefore is presented purely by way ofillustration, and is not to be construed as defining the only conditionscontemplated as being within the scope of the invention.

EXAMPLE 1 Polyvinyl alcohol (PVA) in the form of an aqueous solution of5 percent solids concentration by weight, and polyacrylic acid (PAA) inthe form of an aqueous solution of 7 percent solids concentration byweight, were mixed in proportions to give a solution containing equalweights of the two polymers. Mixing was accomplished by stirring at roomtemperature for about 10 minutes. An antifoam agent (Dow CorningAntiform .A") was added in amount of 0.5 percent volume, to help removeair bubbles. Other known antifoam agents such as Du- Pont Lorol 20 orothers may be used instead, with similar results.

The resulting mixture was allowed to stand to eliminate any trapped airor sediment.

The PVA-PAA solution was then extruded into a horizontal heated trough,containing a coagulating solution. The coagulating solution was anaqueous solution containing 425 grams of sodium sulfate and 20 grams ofzinc sulfate per liter of water. This solution was kept at 40 C. by theuse of an external jacket of resistance-heating tape.

Fibers were prepared by extruding the PVA-PAA solution through ahypodermic needle with the end ground square into the coagulating bath.

The coagulated fibers were allowed to air dry by hanging them in the airunder slight tension provided by small weights. AFter the fibers weredry, they were heated in an oven at l 20 C. to C. for approximately 1hour to effect cross-linking. They may be heated for a time as short asone-half hour or as long as 2 hours, depending on the degree ofcross-linking desired. The fibers were then soaked in water and dilutel- Cl to remove the salts. They were then again dried by hanging them inair with small weights attached. In both drying steps, the function ofthe weights was merely to keep the fibers straightthey were notsufficiently large to stretch the fibers appreciably. The finishedfibers ranged from about 0.003 to about 0.005 inch in diameter.

The finished fibers were cut into 4-cm. lengths and cemented with asilicone rubber adhesive to stainless steel end pieces to produce anassembled sensing element.

The sensing element was seasoned by immersing it several timesalternately in dilute hydrochloric acid (0.015N.) and dilute sodiumhydroxide (0.0l2N.), each immersion being for between about 6 and about18 hours. The purpose of the seasoning is to stabilize the fibers andprevent delayed creep. The length of the seasoned fibers was about 4.30cm.

The seasoned sensing element was then tested by immersing it in water,varying the hardness of the water to simulate the changes occurring overa complete water-softening and regeneration cycle, and the correspondingchanges in the length of fibers of the sensing element were measured.The results, which are shown graphically in FIG. 6, illustrate that whenthe calcium ion concentration was low, indicated on the left-hand scaleby a water hardness of -10 p.p.m. hardness, the fiber length remainedbetween about 4.28 and 4.30 cm., as indicated on the right-hand scale.When the water hardness rose to slightly more than 40 p.p.m. the lengthof the fibers contracted rapidly to slightly more than 4.10 cm. When thehardness of the water was again reduced, the fibers rapidly relaxed toregain their original length. This change in fiber length in response tochanges in water hardness has been found to be rapid, reproducible andreliable, so that a sensing element of the type described is admirablysuited to control of water-softening systems as described earlierherein.

EXAMPLE 2 glass plates and cross-linked by heating at 130 for 90minutes.

Solutions of mixed polymers were also extruded into a salt bathcontaining 425 g. Na SO and 20 g. ZnSO per liter H O at 40 C. through a24 gauge needle. The fibers were air-dried and cross-linked at 90l30from 5 minutes to 3 hours. The degree of cross-linking determined fromtitrations with dilute NaOl-l and dilute HCl using a pH glass electrodefell between 20 and 90 percent. The percent elongation varied frompercent to 0.2 percent, respectively, within those extremes of pH.

EXAMPLE 3 A 5 percent solution of Gantrez AN-l 19, (General Anilineproduct), a commercially available copoly (maleic anhydridemethyl vinylether) was comixed with a 5 percent solution of polyvinyl alcohol withheating and stirring. Solutions were metered to form polymer mixturescontaining 25, 50, and 75 percent polyvinyl alcohol. The solutions werepoured on glass plates and allowed to air dry. The dried films werecured at for 24 hours.

Strips of the interpolymer product contract and expand reversibly (16.7percent of original linear dimension) in alternating dilute solutions ofcalcium ion and sodium ion.

While this invention has been described with reference to certainpreferred embodiments and illustrated by way of certain drawings andexamples, these are illustrative only, as many alternatives andequivalents will readily occur to those skilled in the art, withoutdeparting from the spirit or proper scope of the invention. Theinvention is therefore not to be construed as limited, except as setforth in the appended claims.

What is claimed is:

l. A control device for activating a switch, comprising in combinationsensing means, said sensing means comprising a contractile sensingelement sensitive to the concentration of ions in a body of watersurrounding said sensing element, and control means responsive to saidcontractile sensing element for activating said switch in response to apredetermined change in the length of said contractile sensing element.

2. A control device according to claim 1 wherein said contractilesensing element comprises a contractile fiber, said contractile fiberbeing a copolymer of polyvinyl alcohol and polg acrylic acid.

A control device according to claim 1, wherern said control meansresponsive to said contractile sensing element comprises a magnetmechanically linked to said contractile sensing element, the position ofsaid magnet being variable in response to changes in the length of saidcontractile element, and switch means responsive to changes in theposition ofsaid magnet.

4. A sensing element useful in control apparatus for watertreatingapparatus, comprising in combination at least one contractile fiberhaving a variable length responsive to the concentration of calcium ionsin a body of water surrounding said fiber, and a pair of end fittings onsaid fiber adapted to immobilize one end of said fiber and to transmitto associated control apparatus changes in the position of the other endof said fiber.

5. The control device of claim 4 wherein said means is a reed switch.

1. A control device for activating a switch, comprising in combinationsensing means, said sensing means comprising a contractile sensingelement sensitive to the concentration of ions in a body of watersurrounding said sensing element, and control means responsive to saidcontractile sensing element for activating said switch in response to apredetermined change in the length of said contractile sensing element.2. A control device according to claim 1, wherein said contractilesensing element comprises a contractile fiber, said contractile fiberbeing a copolymer of polyvinyl alcohol and polyacrylic acid.
 3. Acontrol device according to claim 1, wherein said control meansresponsive to said contractile sensing element comprises a magnetmechanically linked to said contractile sensing element, the position ofsaid magnet being variable in response to changes in the length of saidcontractile element, and switch means responsive to changes in theposition of said magnet.
 4. A sensing element useful in controlapparatus for water-treating apparatus, comprising in combination atleast one contractile fiber having a variable length responsive to theconcentration of calcium ions in a body of water surrounding said fiber,and a pair of end fittings on said fiber adapted to immobilize one endof said fiber and to transmit to associated control apparatus chanGes inthe position of the other end of said fiber.
 5. The control device ofclaim 4 wherein said means is a reed switch.